Display device and method of fabricating the same

ABSTRACT

A constitution of the display device of the invention is shown in the following. The display device includes a pixel unit including TFTs of which the active layer contains an organic semiconductor material for forming channel portions in the opening portions in an insulating layer arranged to meet the gate electrodes. The pixel unit further includes a contrast media formed on the electrodes connected to the TFTs for changing the reflectivity upon the application of an electric field, or microcapsules containing electrically charged particles that change the reflectivity upon the application of an electric field. The pixel unit is sandwiched by plastic substrates, and barrier layers including an inorganic insulating material are provided between the plastic substrates and the pixel unit. The purpose of the present invention is to supply display devices which are excellent in productivity, light in weight and flexible.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a display device using contrast media whichchange the reflectivity upon the application of an electric field. Inparticular, the invention relates to a display device formed bycombining a substrate of an organic resin film with thin filmtransistors (hereinafter referred to as TFTs) and the contrast media, aswell as to a method of fabricating the same.

2. Description of the Related Art

Unlike means that uses a cathode-ray tube, a display device that forms ascreen on a flat plate is designed to give electric signals to pixelswhich are arranged in nearly a two-dimensional manner, and to impartbrightness and density by utilizing electro-optical properties of liquidcrystals or light-emitting properties of electroluminescence medium,thereby to display an image. Attention has now been given to the displaydevice of this kind which is a new type of display medium by using anelectrophoretic material filled in microcapsules.

The contrast medium with a form of microcapsule, which can beelectronically addressed is also called electronic ink. Referring toFIG. 10, the electronic ink includes microcapsules 706 of a diameter ofabout 80 μm in which are contained a transparent liquid, fine whiteparticles 701 which are positively charged and fine black particles 702which are negatively charged. When the microcapsules 706 are placed inan electric field, the fine white particles 701 and the fine blackparticles 702 migrate in the opposite directions. When a positive ornegative electric field is applied between an counter electrode(transparent electrode) 703 and pixel electrodes 704, 705 as shown inFIG. 10, fine white particles or fine black particles appear on thesurface to display white or black color, respectively. The electronicink and the counter electrode (transparent electrode) can be formed by aprinting method; i.e., the electronic ink is printed onto a circuitsubstrate to form a display device.

The display device using the electronic ink has an advantage in that itconsumes less electric power than the liquid crystal display device,owing to its reflectivity of about 30% which is several times as much asthat of the reflective liquid crystal display devices. Due to its lowreflectivity, the reflective liquid crystal display devices areadvantageous in places of intense light such as in the sunshine, butneeds an auxiliary illumination such as a front light in a place of weaklight. On the other hand, the display device using the electronic inkneeds no front light owing to its high reflectivity. The front lightneeds an electric power of several hundreds mW, which, however, is notrequired by the display device using the electronic ink. Further, whencontinuously driven on direct current drive, the liquid crystals aredeteriorated. Therefore, the liquid crystal displays must be driven inan alternately inversing manner on alternating current drive. When thefrequency of inversion is low, however, there appears flickering whichis offensive to see. Usually, therefore, the inversion drive isconducted on alternating current drive of from 60 to 100 Hz. The displaydevice using the electronic ink is not required to be driven in aninverting manner on alternating current drive unlike the liquid crystaldisplays and, hence, there is no need of effecting the writing everytime at 60 Hz. The above-mentioned two points make it possible todecrease the consumption of electric power.

In connection with the electronic ink, electrophoretic display devicesusing, for example, amorphous silicon (a-Si) TFTs have been reported in“12.1 “SVGA Microencapsulated Electrophoretic Active Matrix Display forInformation Appliances SID01 DIGEST pp. 152-155” and “A ConformableElectronic Ink Display using a Foil-Based a-Si TFT Array, SID01, DIGESTpp. 157-159”.

The above display device using the electronic ink is based on a simpleprinciple and requires no illumination means that is used in the liquidcrystal display devices and is, hence, called electronic paper, and hasbeen studied concerning its widespread use to substitute for theconventional data transmission or recording means using papers asrepresented by newspapers and books.

In order for the electronic paper to be widely used in the society,means is necessary for supplying a display medium of large areas thatcan be folded like a newspaper at high speeds, in large amounts and atlow prices just like printing characters and photographs on a paper.However, though the TFTs using the inorganic semiconductor layer can beproduced based on an established technology maintaining stability, it isstill necessary to forma semiconductor layer that serves as an activelayer and to form a metal film for forming wirings and electrodes byutilizing vacuum like in the conventional semiconductor process, therebyto form a pattern through the photolithography

Further, in order for the users to enjoy the convenience of handling, itis not desired to use, as a substrate, brittle materials such as aglass, heavy and poorly flexible materials such as a stainless steel. Aflexibility can be maintained to some extent when a thin plate such asof a stainless steel or aluminum is used as a substrate making, however,it is difficult to maintain flatness of the plate surface due to plasticdeformation.

SUMMARY OF THE INVENTION

This invention was accomplished in view of the above problems, and itsobject is to provide a light and flexible display device that can befavorably produced.

In order to solve the above problems, the constitution of the inventionhas a pixel unit which includes TFTs of which the active layer includesan organic semiconductor material for forming channel portions in theopening portions in an insulating layer arranged to meet the gateelectrodes. The pixel unit further includes a contrast media formed overthe electrodes connected to the TFTs for changing the reflectivity uponthe application of an electric field, or microcapsules containingelectrically charged particles that change the reflectivity upon theapplication of an electric field. The pixel unit is sandwiched byplastic substrates, and barrier layers including an inorganic insulatingmaterial are provided between the plastic substrates and the pixel unit.

Another constitution has a pixel unit which includes TFTs of which theactive layer includes an organic semiconductor material for formingchannel portions in the opening portions of an insulating layer arrangedto meet the gate electrodes. The pixel unit further includes a contrastmedia formed over the electrodes connected to the TFTs for changing thereflectivity upon the application of an electric field, or microcapsulescontaining electrically charged particles that change the reflectivityupon the application of an electric field, the contrast media or themicrocapsules being surrounded by a partitioning layer including aninsulating material covering the peripheries of pixel electrodes. Thepixel unit is sandwiched by plastic substrates, and barrier layersincluding an inorganic insulating material are provided between theplastic substrates and the pixel unit.

Another constitution of the invention has a pixel unit which includesTFTs of which the active layer includes an organic semiconductormaterial for forming channel portions in the opening portions in aninsulating layer arranged to meet the gate electrodes. The pixel unitfurther includes a contrast media formed over the electrodes connectedto the TFTs for changing the reflectivity upon an application of anelectric field, or microcapsules containing electrically chargedparticles that change the reflectivity upon the application of anelectric field. The pixel unit is sandwiched by substrates, and barrierlayers including an inorganic insulating material are provided betweenthe substrates and the pixel unit.

Another constitution has a pixel unit which includes TFTs of which theactive layer is includes an organic semiconductor material for formingchannel portions in the opening portions of an insulating layer arrangedto meet the gate electrodes. The pixel unit further includes a contrastmedia formed over the electrodes connected to the TFTs for changing thereflectivity upon an application of an electric field, or microcapsulescontaining electrically charged particles that change the reflectivityupon an application of an electric field, the contrast media or themicrocapsules being surrounded by a partitioning layer including aninsulating material covering the peripheries of pixel electrodes. Thepixel unit is sandwiched by substrates, and barrier layers including aninorganic insulating material are provided between the substrates andthe pixel unit.

In the above constitution of the invention, the plastic substrate hasflexibility and is the one of polyethylene terephthalate (PET),polyethylene naphthalate (PEN), polyether sulfone (PES), a polycarbonate(PC) or a polyimide. These substrates are transparent for visible lightand may have a practicable thickness of 10 to 200 μm to exhibitflexibility. Thus, there is provided a display device which is light inweight exhibiting excellent shock resistance.

It is further desired that the barrier layer formed on the plasticsubstrate is made of AlO_(x)N_(1-x) (where x=0.01 to 0.2) or a siliconnitride without containing hydrogen formed by a RF sputtering. Theinorganic insulating material serves as a barrier layer against thewater vapor or organic gases that infiltrate from the externalenvironment, and prevents the organic semiconductor material thatconstitutes the display device, the contrast medium which changes itsreflectivity upon the application of an electric field, and themicrocapsules containing charged particles that change the reflectivityupon the application of an electric field, from being deteriorated bythe water vapor or the organic gases.

The TFTs formed in the pixels may include an inorganic semiconductormaterial as represented by amorphous silicon but is, here, include anorganic semiconductor material that can be formed by a printing methodthat is capable of supplying a display medium of a large area in largeamounts and at decreased costs like printing characters and photographson a paper without relying upon vacuum technology such as vapor growth.Not only the semiconductor layer but also the electrically conductivelayer such as gate electrodes and the insulating layer such as gateinsulating film may include an organic compound material to accomplishthe object.

The thus constituted display device of the invention is fabricatedthrough the following steps. The first step is forming a barrier layerincluding an inorganic insulating material on the first plasticsubstrate by sputtering. The second step is forming gate electrodesusing an electrically conductive paste formed being patterned on thebarrier layer. The third step is forming the first insulating layer onthe gate electrodes. The fourth step is forming the second insulatinglayer having opening portions on the first insulating layer. The secondinsulating layer is formed so as to correspond to the gate electrodes.The fifth step is forming an organic semiconductor layer in the openingportions. The sixth step is forming source and drain electrodes usingthe electrically conductive paste that is applied being so patterned asto be connected to the organic semiconductor layer. The seventh step isforming the third insulating layer having opening portions formed oneither the source electrodes or the drain electrodes. The eighth step isforming pixel electrodes connected to the source and drain electrodesusing the electrically conductive paste applied in a patterned manner.The ninth step is forming the fourth insulating layer having openingportions covering the ends of the pixel electrodes. The tenth step isforming a resin layer containing, in the opening portions thereof,microcapsules that contain electrically charged particles. The eleventhstep is adhering, onto the resin layer, the second plastic substrate onwhich are formed a barrier layer and a transparent electrode using aninorganic insulating material by sputtering. Here, the first insulatinglayer may function as a gate insulating film.

Among the above steps, the second to ninth steps are for forming basedon the screen-printing method, making it possible to supply a displaymedium having a large area in large amounts and at decreased costs likeprinting characters and photographs on a paper without relying upon thevacuum technology such as vapor growth or the photolithography. Further,upon continuously supplying the flexible and long plastic substrate, itis allowed to continuously conduct the second to eleventh steps toaccomplish a very high productivity. Thus, the invention makes itpossible to provide a display device which is excellent in productivity,light in weight and flexible at a decreased cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view illustrating, in detail, a pixelunit in a display device of the invention.

FIG. 2 is a top view illustrating, in detail, the pixel unit in thedisplay device of the invention.

FIGS. 3A to 3E are vertical sectional views illustrating the steps offabricating the display device of the invention.

FIGS. 4A to 4C are vertical sectional views illustrating the steps offabricating the display device of the invention.

FIG. 5 is a top view illustrating the constitution of the display deviceof the invention.

FIG. 6 is a view illustrating a structure of connection to the TAB at aterminal portion in the display device of the invention.

FIG. 7 is a view illustrating a structure of connection to the TAB atthe terminal portion in the display device of the invention.

FIG. 8 is a view illustrating the constitution of a sputtering devicethat is capable of continuously forming films on a flexible longsubstrate;

FIG. 9 is a diagram illustrating the steps of fabricating a displaydevice of the invention by employing production means by which thesubstrate is continuously delivered and is put to the steps of theprocess, successively.

FIG. 10 is a diagram illustrating the constitution of an electronic inkand its principle.

FIG. 11 is a view illustrating an example where the display device ofthe invention is used in combination with a cellular phone.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will now be described in detail withreference to the drawings. The display device according to the inventionincludes a pixel unit equipped with contrast media which change thereflectivity upon the application of an electric field or an electronicink including microcapsules containing electrically charged particlesthat change the reflectivity upon the application of an electric field,for each of the pixels, the pixel unit further having TFTs forcontrolling the electric field to be applied to each of the pixels. Inthe TFTs, an organic semiconductor material is used as a semiconductorfor forming channel portions, wherein a feature resides in the structurefor separating the semiconductor in the form of islands and in themethod of fabrication. The thus constituted pixel unit is sandwiched bythe plastic substrates.

FIG. 1 is a vertical sectional view illustrating the structure of thepixel unit, and FIG. 2 is a top view thereof. Between plastic substrates101 and 201, there are arranged microcapsules 301 containingelectrically charged particles being sandwiched by organic TFTs usingorganic semiconductor layers 106 a, 106 b, pixel electrodes 110 a, 110 bconnected to the organic TFTs, and a common electrode 203 on the sidefacing thereto. The vertical sectional view shown in FIG. 1 correspondsto the line A-A″ in FIG. 2.

At least either one of the plastic substrate 101 or 201 permits light topass through, and includes a polyethylene terephthalate (PET), apolyethylene naphthalate (PEN), a polyether sulfon (PES), apolycarbonate (PC) or a polyimide. Desirably, the plastic substrate hasflexibility and its practicable thickness is from 10 to 200 μm. Theconstitution of the invention is not essentially affected even byincreasing the thickness to be greater than the above range, as a matterof course.

Barrier layers 102 and 202 including an inorganic insulating materialare formed maintaining a thickness of from 10 to 200 nm on the surfacesof the plastic substrates 101 and 201. The barrier layer has a laminatedlayer structure of one or a plurality of layers being formed ofAlO_(x)N_(1-x) (x=0.01 to 0.2) or a silicon nitride without containinghydrogen formed by RF sputtering method using silicon as a target andnitrogen as a sputtering gas. The inorganic insulating material isdensely formed so as to serve as a barrier layer against the water vaporor organic gases that infiltrate from the external environment. Theobject of forming the barrier layer is to prevent the organicsemiconductor material or the contrast medium that changes itsreflectivity upon the application of an electric field or to prevent themicrocapsules containing electrically charged particles that change thereflectivity upon the application of an electric field, from beingdeteriorated by the water vapor or the organic gases.

The first wiring 103 forming the gate electrode of TFT may be formed ofa known metal material such as aluminum or chromium, or may be formed bythe screen-printing method or the roll-coater method by using anelectrically conductive paste. Further, the first insulating layer 104used as gate-insulating films, second insulating layer 105 and thirdinsulating layer 109 are formed of those materials to which are added anacrylic resin, a polyimide resin, a polyamide resin, a phenoxy resin, anonaromatic polyfunctional isocyanate or a melamine resin. Thegate-insulating film is not necessarily limited to the organicinsulating material but may be a silicon oxide film (SOG: spin on glass)formed by coating method or a silicon oxide film formed by sputteringmethod.

An opening portion formed in the second insulating layer 105corresponding to the gate electrode is for forming an organicsemiconductor layer therein. The organic semiconductor layer is formedby the printing, spraying, spin-coating or ink jet method. As theorganic semiconductor material used in the invention, there is desirablyused a π-electron conjugated high-molecular material of which the bondincludes constituted by the conjugated double bond. Concretely, therecan be used a soluble high-molecular material such as a polythiophene, apoly(3-alkylthiophene), or a polythiophene derivative.

As other organic semiconductor materials that can be used for theinvention, there can be formed organic semiconductor layers that areobtained by forming soluble precursors followed by the treatment. As theorganic semiconductor materials formed through the precursors, there canbe exemplified a polythienylene vinylene, a poly(2,5-thienylenevinylene), a polyacetylene, a polyacetylene derivative and apolyallylene vinylene.

To convert the precursor into an organic semiconductor, not only theheat treatment is effected but also the reaction catalyst is added suchas a hydrogen chloride gas. When this processing is conducted, therearouses a problem of corrosion of the electrodes. In the structure ofthe organic TFTs of the present invention, however, there is no need ofworrying about the above problem. As typical solvents for dissolvingthese soluble organic semiconductor materials, there can be usedtoluene, xylene, chlorobenzene, dichlorobenzene, anisole, chloroform,dichloromethane, γ-butyl lactone, butyl cellosolve, cyclohexane, NMP(N-methyl-2-pyrrolidone), cyclohexanone, 2-butanone, dioxane,dimethylformamide (DMF) and THF (tetrahydrofuran).

Second wirings 107 a, 107 b and third wirings 108 a, 108 b work assource electrodes and drain electrodes of TFTs upon contact with theorganic semiconductor layers. As a material for forming these wirings,it is desired to use a metal having a large work function for obtainingan ohmic contact with the semiconductor layers, since many organicsemiconductor materials for transporting the electric charge are p-typesemiconductors that transport positive holes as carriers.

Concretely, it is desired to use a metal such as gold, platinum,chromium, palladium, aluminum, indium, molybdenum or nickel, or an alloythereof. The second wirings 107 a, 107 b and third wirings 108 a, 108 bare formed by printing or a roll coater by using an electricallyconductive paste containing the above metal or the alloy. Pixelelectrodes 110 a and 110 b, too, are similarly formed on the thirdinsulating layer 109.

The fourth insulating layer is formed so as to cover the ends of thepixel electrodes 110 a and 110 b, and serves as a partitioning layer forsectionalizing the neighboring pixels. An electronic ink layer 302 isformed by the wet-coating such as sprinkling, spin-coating, printing ora roll coater, so as to be filled in the opening portions of the fourthinsulating layer, i.e., so as to be filled among the partitioninglayers. On the electronic ink layer, there are formed a barrier layer202 including an inorganic insulating material formed on the plasticsubstrate 201, and a transparent electrically conductive film 203 suchas of indium-tin oxide or zinc oxide.

The microcapsules 301 contained in the electronic ink layer 302 containparticles of a given color that are positively charged and particles ofa different color that are negatively charged, the particles beingdispersed in a solvent contained in the microcapsules. Depending upon anelectric field imparted by the pixel electrodes, particles of a givencolor or particles of another color are segregated in one direction,changing the contrast depending upon the individual pixels thereby todisplay an image.

Steps for fabricating the display device of the invention for displayingan image by changing a contrast in the electronic ink layer, will now bedescribed with reference to FIGS. 3 and 4.

In FIG. 3A, the barrier layer 102 of aluminum oxynitride(AlO_(x)N_(1-x): x=0.01 to 0.2) or silicon nitride is formed on theplastic substrate 101 by RF sputtering method. The aluminum oxynitrideis formed by using aluminum nitride as a target and by using asputtering gas obtained by suitably mixing argon as well as oxygen andnitrogen, while suitably setting the mixing ratio of oxygen such thatthe oxygen content in the aluminum oxynitride film is from 0.01 to 20atomic %. The silicon nitride is formed by using silicon as a target andby using nitrogen only as a sputtering gas. These inorganic insulatinglayers are capable of forming a sense inorganic insulating layer suitedas a barrier layer. By selecting the thickness to be from about 10 toabout 100 nm, the barrier layer exhibits gas-barrier property againstwater vapor and organic gases.

The first wiring 103 formed thereon works as a gate electrode of theTFT, and is formed by using an electrically conductive paste. As theelectrically conductive paste, there is used electrically conductivecarbon paste, electrically conductive silver paste, electricallyconductive copper paste, or electrically conductive nickel paste, whichis formed into a predetermined pattern by screen-printing or aroll-coater. The predetermined pattern that is formed by using theelectrically conductive paste is, then, subjected to leveling, dryingand curing at 100 to 200° C. to obtain a layer which is 1 to 5 μm thick.

FIG. 3B illustrates a step of forming the first insulating layer 104that serves as the gate-insulating film by a roll-coater or spraying,and including an organic insulating material to which are added acrylicresin, polyimide resin, phenoxy resin, nonaromatic polyfunctionalisocyanate and melamine resin, or including silicon oxide film (SOG:spin on glass) formed by coating or including silicon oxide film formedby sputtering. It is desired that the gate-insulating film is formedmaintaining a thickness of from about 100 to about 200 nm by taking agate voltage into consideration, but there is no particular problem evenwhen the thickness is greater than the above range.

Referring to FIG. 3C, the second insulating layer 105 is formed byscreen-printing having opening portions formed in the regions that meetthe positions of the first wiring 103. There is suitably used an organicinsulating material to which are added acrylic resin, polyimide resin,polyamide resin, phenoxy resin, nonaromatic polyfunctional isocyanateand melamine resin, being formed maintaining a thickness of about 0.1 toabout 3 μm. The second insulating material having such opening portionsis formed by forming an insulating layer on the whole surface byspin-coating and, then, forming opening portions by photolithography. Inany way, opening portions are formed and an organic semiconductor layeris formed therein, without requiring the step of etching that isnecessary for forming a pattern for isolating, maintaining insulation,the organic semiconductor layers having low water resistance for each ofthe TFTs.

FIG. 3D is for forming the organic semiconductor layers 106 a and 106 bby printing, spraying, spin-coating or ink-jet method so as to meet theopening portions. The illustrated shape may be formed by Damascenemethod by forming an organic semiconductor layer so as to fill theopening portions in the second insulating layer and, then, polishing thesurface leaving the organic semiconductor layer in the opening portions.

In FIG. 3E, the second wirings 107 a, 107 b and the third wirings 108 a,108 b are formed by using the electrically conductive paste like thefirst wirings. The second wirings and the third wirings are formed beingpartly overlapped with the organic semiconductor layers 106 a, 106 b soas to work as sources and drains.

In FIG. 9A, the third insulating layer 109 is formed by thescreen-printing method like other insulating layers having openingportions formed on the third wirings 108 a, 108 b. After formed into apredetermined pattern, the third insulating layer 109 is subjected toleveling, drying and, then, curing at 100 to 200° C. to obtain a layerwhich is 1 to 5 μm thick. Then, an electrically conductive paste isprinted to form pixel electrodes 110 a and 110 b. The pixel electrodesneed not permit light to pass through, and are formed by usingelectrically conductive carbon paste, electrically conductive silverpaste, electrically conductive copper paste or electrically conductivenickel paste.

Then, in FIG. 4B, the fourth insulating layer 111 is formed so as tocover the peripheries of the pixel electrodes 110 a, 110 b, formingopening portions therein in a manner to be just located on the pixelelectrodes. The fourth insulating layer 111 sectionalizes the pixelregions and works as a partitioning layer. The insulating materialthereof and the forming method thereof may be the same as those of otherinsulating layers and it is desired to disperse therein carbon black orblack pigment. With the neighboring pixels being thus sectionalized, itis allowed to eliminate crosstalk and to make the image vivid by addinga function as black stripes of the liquid crystal display device. Thearea of the opening portion may be suitably determined, e.g., 100×400 μmto contain one or a plurality of pixel electrodes of microcapules of theelectronic ink.

Referring to FIG. 4C, the electronic ink layer 302 is formed byroll-coater method, printing or spraying. Then, as shown in FIG. 1, theplastic substrate 201 on which the barrier layer 202 and the commonelectrode 203 including the transparent electrically conductive film isformed, is adhered thereon. If a positive or negative voltage is applieddue to a switching operation of the TFT connected to the pixel electrodewhile maintaining the potential of the common electrode 203 constant,the microcapsules 301 in the electronic ink layer react thereto, wherebycolored particles which are negatively or positively charged segregatetoward one side to display an image. Video signals may be input to thepixels through a driver circuit arranged by using a TAB or COG though itmay vary depending upon the ability for driving the TFTs formed with theorganic semiconductor layer.

FIG. 5 is a diagram illustrating the constitution of the display deviceof the invention, wherein a pixel 503 of one unit is constituted by acombination of a TFT 504 formed by the organic semiconductor layer and acontrast medium 505 connected thereto over the plastic substrate 101.The pixels are arranged in the form of a matrix to constitute a pixelunit 502. The driver ICs 508 are mounted by TABs 506, 507.

The TABs 506 and 507 can be connected from the backside of the plasticsubstrate 101 on where there are formed none of the organicsemiconductor layer or the electronic ink layer. The connection portionsmay slightly differ between the TAB 507 on the side of the scanning lineand the TAB 508 on the side of the signal line. Its details are shown inFIGS. 6 and 7.

FIG. 6 is a diagram illustrating the connection of the TAB 507 connectedto the side of the scanning line, wherein the TAB 507 is connected tothe gate wiring 103 through an anisotropic electrically conductiveadhesive 304. To make the connection, an opening portion 300 is formedin the plastic substrate 101 and in the barrier layer 102 to expose thefirst wiring 103 that forms the scanning line. Referring to FIG. 7, onthe other hand, the TAB 506 that connects to the signal line isconnected, through an anisotropic electrically conductive adhesive 304,to the second wiring 107 that forms the signal line. To make theconnection, an opening portion 300 is formed in the plastic substrate101, barrier layer 102, first insulating layer 104 and second insulatinglayer 105 to expose the second wiring 107. The opening portion 300 canbe formed by laser process, such as of Nd:YAG laser. It is most desiredthat the opening portion is so formed that the surfaces of the wiringsare exposed as shown. When it is difficult to carry out the selectiveprocess, the plastic substrates 101 and 102 may be penetrated through.In this case, a sealing pattern 303 formed of an adhesive resin issuperposed on a position where the opening portion is formed to maintainair-tightness without affecting the electronic ink layer 302.

As described above, the display device of this invention is fabricatedmainly by printing or roll-coater method employing plastic substrateshaving flexibility capable of spectacularly improving productivity. Thatis, by using the long sheet-like substrate that is rolled, there can beapplied production means called roll-to-roll method by which thesubstrate is continuously delivered and the processing is continuouslyconducted in order of steps.

The steps of production in this case can be divided into the steps offorming the barrier layers that require the vacuum processing due to theuse of aluminum oxynitride or silicon nitride, and the steps of formingthe organic semiconductor layer and the first to fourth insulting layersunder the atmospheric pressure by printing. If the atmospheric-pressureplasma CVD technology is employed for forming the barrier layers, all ofthe steps can be carried out under the atmospheric pressure.

FIG. 8 illustrates the constitution of a sputtering device capable ofcontinuously forming a film on an long flexible substrate by theroll-to-roll method. Rolls 802 and 803 winded with a long flexiblesubstrate are provided in a film-forming chamber 801. The long flexiblesubstrate is delivered from one roll to the other roll as they arerotated being interlocked together. The film is formed by decreasing thepressure in the film-forming chamber 801 by evacuation means 809, bysupplying the sputtering gas from gas supply means 810, and byestablishing a glow discharge by supplying a DC or AC electric power tothe targets 804 and 814 from the power sources 806 and 816. The targets804 and 814 are cooled by cooling means 808 which supplies a coolant,and heating means 805 and 815 are used when it is necessary to heat thesubstrate.

The targets 804 and 814 may be suitably selected depending upon the filmto be deposited. When the aluminum oxynitride film is to be formed, thealuminum nitride is used as a target, and a mixed gas of argon, nitrogenand oxygen is used as a sputtering gas. When the silicon nitride film isto be formed, silicon is used as a target, and nitrogen is used as asputtering gas.

To laminate the barrier layer 202 and the common electrode 203 on theplastic substrate 201 as shown in FIG. 1, the target of aluminum nitrideand the target of indium-tin oxide (ITO) may be provided beingjuxtaposed to each other to continuously form them.

FIG. 9 illustrates the steps for forming the organic semiconductor layerand the first to fourth insulating layers as well as the TFTs and theelectronic ink layer. The plastic substrate on which the barrier layeris formed is continuously supplied from a roll 901, or is intermittentlydelivered by a step-by-step method. The subsequent steps are forprinting the first wiring and firing thereof, printing the firstinsulator and firing thereof, printing the second insulator and firingthereof, printing the organic semiconductor and firing thereof, printingthe second and third wirings and firing thereof, printing the thirdinsulator and firing thereof, printing the pixel electrodes and firingthereof, printing the fourth insulator and firing thereof all by using ascreen-printing device 902 and a firing apparatus 903, and applying thecontrast medium. Then, a plastic substrate on which the barrier layerand the common electrode are formed is continuously supplied from a roll905, and is adhered, by sticking means, onto the substrate onto which upto the contrast medium have been applied. A step of processing theterminals is conducted by a laser processing apparatus 907.

Through the above steps, a plurality of pixel units are continuouslyformed on the long substrate. In the final step of cutting, thesubstrate is cut by a cutting device 908 into individual pixel units tothereby obtain a basic constituent unit 909 of the display device of theinvention. Here, the long substrate on which the pixel unit are formedmay be once rolled, and then, may be delivered and cut into individualpixel units. Then, a driver IC may be mounted.

From the standpoint of improving convenience, there has been proposed anidea of a system-on-panel integrating all of the pixel units forvisually displaying the data on a piece of panel, a communicationfunction for transmitting and receiving a variety of data, and acomputer function for storing or processing the data. On the other hand,the display device of the invention which is light in weight, thin,flexible and tough, can be so designed as to place particular importanceon the display function.

FIG. 11 is a view illustrating the use in combination with a cellularphone. The cellular phone includes a main body 601, a housing 602, adisplay unit 603, a voice input unit 604, a voice output unit 605, anoperation key 606, an infrared-ray communication means 607, and anantenna 608. The display device may be incorporated in the housing, andincludes a main body 610, a pixel unit 611 for displaying an image, adriver IC 612, a receiver device 613 and a film battery 614. The driverIC and the receiver device are mounted by using semiconductor parts.Here, the data processing function is carried out by utilizing thecellular phone and, hence, the display device needs bear a decreasedload. The display device of the invention makes it possible for the userto freely carry a display medium of a large screen with him.

The display device of the invention can be further used mainly as meansfor displaying still image from such uses as navigation systems,acoustic reproduction devices (car audio, audio components, etc.),personal computers, game devices, portable data terminals (mobilecomputers, cellular phones, portable game devices, electronic books,etc.) through such domestic appliances as refrigerators, washingmachines, rice cookers, stationary telephones, vacuum cleaners, clinicalthermometers up to information displays of large areas such asadvertisements hanging in the trains, arrival/departure guide boards atthe railway stations and at the airports, etc.

Though preferred embodiments of the invention were described above, itwill be easy for people skilled in the art to modify and change theembodiments and details thereof in a variety of ways without departingfrom the gist and scope of the invention.

The invention provides a display device that can be favorably produced,is light in weight and is flexible. In particular, the invention makesit possible to realize a display device which is light in weight and isflexible by forming all of the portions, except the barrier layers, byusing an organic compound material. From the standpoint of productiontechnology, further, the invention much uses the screen-printing makingit possible to supply a display medium of a size of a newspaper in largeamounts and at decreased costs like printing characters and photographson a paper without relying upon the vacuum technology such as vaporgrowth or the photolithography.

1. (canceled)
 2. A display device comprising: a substrate; a firstinsulating layer comprising nitrogen over the substrate; a gateelectrode over the first insulating layer; a gate insulating layer overthe gate electrode; a semiconductor layer over the gate insulatinglayer; a source electrode and a drain electrode over the semiconductorlayer; a second insulating layer comprising resin over the sourceelectrode and the drain electrode; a pixel electrode over the secondinsulating layer; and a layer comprising a microcapsule over the pixelelectrode, wherein one of the source electrode and the drain electrodeis electrically connected to the pixel electrode, wherein the pixelelectrode and the other one of the source electrode and the drainelectrode are overlapped with each other, and wherein the pixelelectrode and the gate electrode are overlapped with each other.
 3. Thedisplay device according to claim 2, wherein the first insulating layercomprises silicon nitride.
 4. The display device according to claim 2,wherein the semiconductor layer comprises an organic semiconductormaterial.
 5. The display device according to claim 2, wherein the secondinsulating layer comprises any of an acrylic resin, a polyimide resin, apolyamide resin, and a phenoxy resin.
 6. The display device according toclaim 2, wherein the pixel electrode and the one of the source electrodeand the drain electrode are overlapped with each other.
 7. The displaydevice according to claim 2, wherein the substrate has flexibility.
 8. Adisplay device comprising: a substrate comprising polyimide; a firstinsulating layer comprising nitrogen over the substrate; a gateelectrode over the first insulating layer; a gate insulating layer overthe gate electrode; a semiconductor layer over the gate insulatinglayer; a source electrode and a drain electrode over the semiconductorlayer; a second insulating layer comprising resin over the sourceelectrode and the drain electrode; a pixel electrode over the secondinsulating layer; and a layer comprising a microcapsule over the pixelelectrode, wherein one of the source electrode and the drain electrodeis electrically connected to the pixel electrode, wherein the pixelelectrode and the other one of the source electrode and the drainelectrode are overlapped with each other, and wherein the pixelelectrode and the gate electrode are overlapped with each other.
 9. Thedisplay device according to claim 8, wherein the first insulating layercomprises silicon nitride.
 10. The display device according to claim 8,wherein the semiconductor layer comprises an organic semiconductormaterial.
 11. The display device according to claim 8, wherein thesecond insulating layer comprises any of an acrylic resin, a polyimideresin, a polyamide resin, and a phenoxy resin.
 12. The display deviceaccording to claim 8, wherein the pixel electrode and the one of thesource electrode and the drain electrode are overlapped with each other.13. The display device according to claim 8, wherein the substrate hasflexibility.
 14. A display device comprising: a substrate comprisingpolyimide; a first insulating layer comprising nitrogen over thesubstrate; a gate electrode over the first insulating layer; a gateinsulating layer over the gate electrode; a semiconductor layer over thegate insulating layer; a source electrode and a drain electrode over thesemiconductor layer; a second insulating layer comprising resin over thesource electrode and the drain electrode; a pixel electrode over thesecond insulating layer; and a layer comprising a microcapsule over thepixel electrode, wherein each of the source electrode and the drainelectrode comprises molybdenum, wherein one of the source electrode andthe drain electrode is electrically connected to the pixel electrode,wherein the pixel electrode and the other one of the source electrodeand the drain electrode are overlapped with each other, and wherein thepixel electrode and the gate electrode are overlapped with each other.15. The display device according to claim 14, wherein the firstinsulating layer comprises silicon nitride.
 16. The display deviceaccording to claim 14, wherein the semiconductor layer comprises anorganic semiconductor material.
 17. The display device according toclaim 14, wherein the second insulating layer comprises any of anacrylic resin, a polyimide resin, a polyamide resin, and a phenoxyresin.
 18. The display device according to claim 14, wherein the pixelelectrode and the one of the source electrode and the drain electrodeare overlapped with each other.
 19. The display device according toclaim 14, wherein the substrate has flexibility.